** Also affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Jammy)
Status: New => Invalid
** Changed in: linux (Ubuntu)
Status: New => Fix Released
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https://bugs.launchpad.net/bugs/2017774
Title:
both dell_backlight and nvidia_0 backlight interface appear, and can't
adjust the display brightness
Status in HWE Next:
New
Status in linux package in Ubuntu:
Fix Released
Status in linux-oem-6.0 package in Ubuntu:
Invalid
Status in linux source package in Jammy:
Invalid
Status in linux-oem-6.0 source package in Jammy:
In Progress
Bug description:
[Impact]
When switched to discrete mode in the BIOS, nvidia driver will create its own
backlight interface(nvidia_0) to control the backlight, but at the same time
dell-laptop creates its own backlight interface(dell_backlight), too. In
discrete mode, dell_backlight interface doesn't work, and it leads to gnome
chooses the wrong interface(dell_backlight) to control the backlight and then
leads to the issue.
[Fix]
The acpi_video_backlight_use_native() helper function is introduced after
v6.1 and nvidia driver will call this function if kernel provides it. This
helper tells video_detect module that nvidia controls the backlight, so that
dell-laptop won't create another backlight interface when it's loaded
Below commits are all from v6.1-rc1
fb1836c91317 ACPI: video: Prefer native over vendor
a5df42521f32 ACPI: video: Simplify
__acpi_video_get_backlight_type()454d61a56d5e ACPI: video: Make
acpi_video_backlight_use_native() always return true
b39be9f441f9 ACPI: video: Refactor acpi_video_get_backlight_type() a bit
a2fc3c899bb0 ACPI: video: Drop backlight_device_get_by_type() call from
acpi_video_get_backlight_type()
2600bfa3df99 ACPI: video: Add acpi_video_backlight_use_native() helper
[Test]
Verified on the target machine and confirmed dell_backlight interface is not
generated.
[Where problem could occur]
All changes are in __acpi_video_get_backlight_type() function and to make it
smarter to decide which type of backlight interface should be created. The
final result is pretty similar to the latest mainline version, if it introduce
any regression we can add quirk to list those misjudged machines.
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